(1) Field of the Invention
The invention relates to the fabrication of integrated circuit devices, and more particularly, to a method and methodology of automatically controlling the process of Chemical Mechanical Polishing (CMP) of a semiconductor surface.
(2) Description of the Prior Art
The first processing step during wafer processing typically is a step of cleaning the wafer surface in order to remove all impurities from the surface of the wafer. After this first step of cleaning is completed, the wafer surface typically is treated with organic compounds, such as acetone, trichloroethylene, methanol and ethanol, to remove organic impurities such as greases or hydrocarbons. As a final step in the cleaning process inorganic chemicals are used. These inorganic chemical mixtures are strong oxidants that form a thin oxide layer on the surface of the semiconductor wafer. As part of this process, this oxide layer is removed thereby removing the impurities that have been absorbed into the oxide layer.
The Chemical Mechanical Polishing process uses commercially available cleaning systems. These cleaning systems use a combination of rotating pads, each pad being in direct physical contact with the wafer surface. Due to a rotating movement of the polishing pad with respect to the wafer surface, the polishing pad planarizes by means of an abrasive action, the surface of the semiconductor wafer. The various turntables used for this purpose typically rotate at various controlled speeds, for instance 10 to 100 RPM, in a controlled clockwise or counterclockwise direction. The wafer is clamped and held, typically face downward, against the rotating polishing pad. The size of the diameter of the polishing pads is typically considerably larger than the size of the diameter of the semiconductor substrate. This means that more than one polishing pad can be arranged to simultaneously polish the surface of the wafer, these polishing pads typically being arranged in a circular patterns around the center of the wafer that is being polished.
Polishing pads are typically fabricated from a polyurethane and/or polyester base material and are commercially available such as models IC1000 or Scuba IV of a woven polyurethane material.
Chemical Mechanical Polishing (CMP) is a method of polishing materials, such as semiconductor substrates, to a high degree of planarity and uniformity. The process is used to planarize semiconductor slices prior to the fabrication of semiconductor circuitry thereon, and is also used to remove high elevation features created during the fabrication of the microelectronic circuitry on the substrate. One typical chemical mechanical polishing process uses a large polishing pad that is located on a rotating platen against which a substrate is positioned for polishing, and a positioning member which positions and biases the substrate on the rotating polishing pad. Chemical slurry, which may also include abrasive materials therein, is maintained on the polishing pad to modify the polishing characteristics of the polishing pad in order to enhance the polishing of the substrate.
Many of the CMP operations and the therewith related operations are being placed under automatic control for reasons of for instance increased throughput, improved performance and reduced cost of the CMP process, improved end-point control, and the like. The invention provides a method that further extends this process of automation of the CMP process by monitoring the in-line removal rate, by using methods of curve-fitting that enable a reduction in the frequency of monitoring the removal rate of the CMP process, by enhancing the life expectancy of the polishing pad thereby further reducing the frequency of the required Preventive Maintenance and by allowing for the polishing of non-standard lots of wafers.
U.S. Pat. No. 5,990,010 (Berman), U.S. Pat. No. 6,120,347 (Sandhu et al.) and U.S. Pat. No. 5,823,853 (Bartels et al.) show Chemical Mechanical Polishing (CMP) tools and control processes.
U.S. Pat. No. 5,433,651 (Lustig et al.) reveals a CMP tool and an in-situ monitoring and control process.